Aromatic polycarbonate polymers are well known and exhibit properties of extreme toughness, transparency, resistance to burning and in general, maintenance of useful properties over a wide temperature range. Although polycarbonates exhibit high impact strength in general, the impact strength decreases at low temperatures and at elevated temperatures after aging of the polymers.
Blends of polycarbonates (PC) with other thermoplastic resins have been sought, therefore, to improve the impact resistance of polycarbonate resins. Typical polymer blends include polycarbonate resins with poly(alkylene terephthalate) resins such as those disclosed in U.S. Pat. No. 4,554,315, U.S. Pat. No. 4,267,096 and EP 0 135 779. Polycarbonate blends with poly(cyclohexylene dimethylene terephthalate) resins (PCT) are also known such as those disclosed in U.S. Pat. No. 4,628,074 and U.S. Pat. No. 4,536,538.
Specifically, U.S. Pat. No. 4,554,312 discloses thermoplastic blends of a polycarbonate resin with a poly(alkylene terephthalate) resin, an acrylic core-shell impact modifier and an epoxide-containing polymer modifier. The preferred poly(alkylene terephthalate) resin is poly(ethylene terephthalate) (PET).
U.S. Pat. No. 4,267,096 discloses blends comprising 65-97.5 parts by weight of an aromatic polycarbonate resin, 1-30 parts by weight of an amorphous polyester resin and 0.1-6 parts by weight of a partially hydrogenated copolymer of a vinyl aromatic compound and a diolefin. The amorphous polyester resin may be a poly(alkylene terephthalate) or a poly(cyclohexylene dimethylene terephthalate) resin.
U.S. Pat. No. 3,864,428 discloses thermoplastic resins comprising 10-75 wt% polycarbonate, 25-85 wt% of an aromatic polyester and 2-35 wt% of a butadiene polymer-vinyl monomer graft copolymer. These resins do not contain PET, however.
EP 0 135 779 discloses polycarbonate blends containing a poly(alkylene terephthalate) resin and an amorphous copolyester copolymer resin which is prepared by reacting terephthalic and/or isophthalic acids with a mixture comprising cyclohexanedimethanol and ethylene glycol in a molar ratio of 4:1 to 1:4, respectively.
U.S. Pat. No. 4,628,074 teaches that polycarbonate compositions containing polycarbonates and a poly(cyclohexylene dimethylene terephthalate) resin with an effective amount of an impact modifier such as an olefin diene terpolymer exhibit improved impact strength. Similarly, U.S. Pat. No. 4,536,538 discloses compositions containing a major amount of an aromatic polycarbonate and a minor amount of an amorphous polyester derived from cyclohexane dimethanol and an aromatic dicarboxylic acid.
Despite considerable efforts, a need still exists for impact modified polyester/polycarbonate blends which exhibit improved impact strength at both high and low temperatures.